Ask HN: Launching a startup in an already saturated market?

I've spent the last few months working on a time/task tracking and invoicing web app. There are obviously TONS of them already out there, many of which already have a dedicated user base, but I really feel like mine does things differently than any I've ever seen (not going into details here since it's not very relevant to this question).

I'm relatively new to the startup game, but it seems like the majority of startups try to execute some big new idea, while mine is just a rework of a bunch of old ideas (like "how time should be entered", or "how tasks should be edited/assigned", etc.)

Any tips on how I can gauge the marketability of my system since everyone is already using a different one? Is there any chance that I could succeed, or should I just keep it to myself and not invest the time/money in trying to make a business out of it (which would be fine with me since it was originally built for myself)?

(I know that without you seeing the app, this question is a little vague, and I apologize for that).